This invention relates to compositions having improved fire retardancy, containing ethylene copolymers.
Polymer compositions containing one or more ethylene polymers, fillers, and optionally other components such as compatibilizers, surfactants, etc. are known. A class of highly filled ethylene copolymer compositions containing processing oils or other compatibilizing agents are available commercially from E. I. du Pont de Nemours and Company, Wilmington, Del. under the name Keldax.RTM.. Several U.S. Pat. Nos. describe such compositions, including U.S. 4,191,798 (Schumacher et al.); 4,222,924 (Schumacher); 4,263,196 (Schumacher et al.); 4,403,007 (Coughlin); 4,438,228 (Schenck); 4,379,190 (Schenck); 4,434,258 (Schumacher); 4,480,061 (Coughlin et al.); 4,472,545 (Coughlin et al.); 4,434,261 (Brugel et al.); and 4,430,468 (Schumacher). Most of those compositions, because of their high level of filler material, usually inorganic filler material, have a certain degree of fire resistance but are mainly used in applications where fire resistance or fire retardancy are not critical requirements. They often are used, for example, as sound deadening automotive carpets or liners.
It would be desirable to have available a highly filled ethylene copolymer composition for uses in which flame retardancy is a critical requirement, for example, in building panels, roofing sheets, electrical wire coverings, etc. However, because of very stringent test requirements, the currently available ethylene copolymer compositions cannot be recommended for such uses. A satisfactory composition must not only possess acceptable mechanical properties at its normal operating temperature but also at high temperatures occurring at the time of fire, so that it will not sag, flow, and eventually ignite. The goal is to obtain on exposure to flame a char structure having good heat insulating properties and mechanical integrity capable of preventing further spread of fire.